John Ferguson thinks he is the "Prince of God." He has thought so for decades. Mr. Ferguson believes that he can't be killed and his body will not remain in a grave. Rather, he will assume his seat at the right hand of God, come back to life, and save America from a communist plot.

John Ferguson suffers from paranoid schizophrenia. In the terminology of the Supreme Court, he is "insane."

Mr. Ferguson was first diagnosed with mental illness nearly 50 years ago. He has spent the last 35 of those years on death row in Florida, following convictions for multiple murders. Mr. Ferguson has been in prison since his convictions, and if his death sentence is commuted, he will remain there for the rest of his life to keep the public safe.

But executing him, as the State plans on Monday, August 5, would violate the U.S. Constitution. In Ford v. Wainwright (1986) and Panetti v. Quarterman (2007), the U.S. Supreme Court held that it is cruel and unusual punishment to execute a person who is insane and lacks a rational understanding of why he is being put to death and the effect of the death penalty.

In fact, states have been prohibited from executing people who are insane since the founding of our nation. It was a principle the colonists carried over from centuries of English common law. In 1680, the English jurist Sir Edward Coke explained: "By intendment of Law the execution of the offender is for example... but so it is not when a mad man is executed, but should be a miserable spectacle, both against Law, and of extream inhumanity and cruelty, and can be no example to others."

Some 300 years later, the U.S. Supreme Court observed: "Whether its aim be to protect the condemned from fear and pain without comfort of understanding, or to protect the dignity of society itself from the barbarity of exacting mindless vengeance, the restriction [against executing the insane] finds enforcement in the Eighth Amendment."

Florida's own doctors have found that Mr. Ferguson suffers from schizophrenia, delusions, and severe mental impairment. He spent most of the 1970s in Florida psychiatric institutions. Seven different psychiatrists - all appointed by the State - concluded he suffers from paranoid schizophrenia and is prone to psychotic hallucinations and delusions.

By 1975, two different doctors warned that Mr. Ferguson "is dangerous to the point where he is considered homicidal [and] should not be released under any circumstances." The State did not follow its own doctors' warnings, and Mr. Ferguson was released about a year later. Unfortunately, the danger that the doctors predicted came to pass.

Mr. Ferguson's case is proof positive of the failings of our mental health system, and if the State of Florida has its way, his execution will chillingly demonstrate the fatal injustices that people with mental illness face in our court system. The Florida courts have found as facts that Mr. Ferguson has a documented history of paranoid schizophrenia; he is not malingering or "faking" his mental illness; and he has a fixed grandiose delusion that he is the "Prince of God." These factual findings should be sufficient to bar his execution as a person who is insane, but Florida has failed to follow controlling U.S. Supreme Court precedent.

Specifically, the Florida Supreme Court found that Mr. Ferguson was competent for execution because he was factually aware of his impending execution. But in Panetti, the U.S. Supreme Court held that mere factual awareness is not enough. The U.S. Supreme Court clearly stated that the Eighth Amendment prohibits a state from executing someone who, like Mr. Ferguson, lacks a rational understanding of the reason for his execution and the effect of that execution.

A judge on the Eleventh Circuit Court of Appeals pointed out that the Florida Supreme Court applied a "patently incorrect" legal standard when it refused to apply the law of the U.S. Supreme Court. For the time being, the Eleventh Circuit has let Florida's ruling stand. Whatever deference the Florida Supreme Court may be due, it is not entitled to ignore the law of the land.

Florida should not be able to deem Mr. Ferguson insane for half a century, and then turn around and say now that he is competent for execution. The U.S. Supreme Court must intervene to ensure Florida adheres to the correct legal standard.

John Ferguson is a very sick, elderly man. His execution would bring fear, pain, barbarism, and mindless vengeance into the world, not justice.